Grantby (spoilers)
At the end of the novel, Grantby is given a department working between (Palmer) and Ross. In the film, his fate is left unknown; Dalby, as a traitor, is shot.
Grantby, whilst also a villain, makes logical sense to turn into a double, at least as far as the book goes.
It would be nice to know if the filmmakers had any plan for working this into the plot; it could have made a interesting twist to have him end up working for the British, although the danger would be in diminishing the effect of the conclusion as it stands.